The Rochester Epidemiology Project (REP) is the medical records linkage system that encompasses the care delivered to residents of Rochester and Olmsted County, Minnesota. By affording access to the detailed inpatient and outpatient medical records of health care providers in the community, this unique data resource is able to provide accurate incidence and trend data over 50 years or more for nearly any disease or syndrome and to support population-based studies of etiology and outcome. It makes possible the efficient implementation of important studies on the epidemiology of heart disease, stroke, dementia, cancer, diabetes, digestive diseases, osteoporosis, arthritis and other disorders that have culminated in 813 publications since the system was organized in 1966 including 353 (261 published; 92 accepted or submitted) in the past four years. Although Mayo Clinic contributes substantially to the support of this database by indexing the medical events cited in its own records at no cost to this project, ongoing extramural support is needed to collect diagnostic data from the non-Mayo providers in the community and to integrate the information from all sources of care into a true population-based data repository. Specifically, continued funding is needed to: (1) enhance and maintain the enumeration and unique identification of Olmsted County residents which serves as the essential core of this data system; (2) continue collecting medical event data (e.g., diagnoses, procedures) from the non-Mayo providers of health care for 1995 through 1999 in order to ensure complete case ascertainment and follow-up; (3) complete and maintain the REP Master file (the relational database which will provide electronic linkage of medical events with the enumerated population of the county) and to begin integrating the increasing volume of electronic information about episodes of medical care and hospitalization, clinical and pathological diagnoses, surgical and diagnostic procedures, laboratory values, prescription drugs and data from specific study files or registries into this database; and (4) improve logistic support for epidemiologic studies by further automating study procedures and by developing additional analytic tools. These activities are indispensable to the continued support of the large body of epidemiologic research that is being conducted in this population by investigators from Mayo Clinic and other centers throughout the country, including 20 separate studies funded by the National Institutes of Health during the previous grant period. These studies have served to increase knowledge of a multitude of disease processes of social significance nationally. Although the basic data system has worked well, these aims will allow the investigators to extend the capabilities of this research infrastructure and to further validate the Rochester Epidemiology Project databases and investigative approaches.